Page:The Zoologist, 4th series, vol 4 (1900).djvu/241

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the large majority of birds are widely distributed over the face of the globe is a fact now well ascertained. Their migratory propensities, which seem to be the rule rather than the exception, account largely for their geographical distribution. But it does not necessarily follow from this that certain species are equally plentiful in different countries; for example, the Redstart is decidedly rare in Ireland, whereas in many parts of the Continent it is quite a plentiful bird. Even in the same country a bird may be common in one province, and unknown in another. Thus, in Kilkenny and Queen's County the Jay is often seen, whereas it is practically absent from Louth and Dublin.

These facts concerning distribution are highly important to those who may wish to determine the absolute rarity of birds, a matter which every collector should consider before attempting to diminish their numbers. A non-breeding casual migratory species, seldom occurring in the British Isles, but common and widely distributed in other countries, cannot in any sense be considered a really rare bird. It is only relatively so, and in the cause of science it seems quite allowable to capture such a species provided that the scientist wishes to advance his knowledge of ornithology. By such a procedure he will not materially lessen the numbers of the species, and moreover he will obtain reliable evidence of the occurrence of a so-called rare native bird. The present article has been written with the view of supporting this idea. The occurrences of different kinds of birds (as many as possible) inhabiting both Ireland and Switzerland are in the first place recorded. Their variation in numbers in the two countries (the question of relative rarity) is then compared. But in all cases one must not expect the numbers to sensibly vary.